(Field of the Invention)
The present invention relates to a heat-collecting-type power generation system.
(Description of the Related Art)
Conventionally, as a power generation system that generates power while collecting low-temperature waste heat, a binary power generation system is well known. This power generation system performs power generation in the following manner: a working medium having a low boiling point is caused to evaporate by utilizing waste heat, and with use of this gas-phase flow of the working medium, a displacement-type expander, for example, a screw type expansion turbine is rotated and driven, whereby a power generator is rotated together with the expander. Further, examples of a heat source from which heat is collected by such a power generation system include a variety of heat sources such as supercharged air to be supplied to a marine engine, waste heat of an engine, waste heat of a thermal power station, an incineration facility, and a factory, etc.
For such a power generation system, a task to be achieved is necessary to improve the power generation efficiency, so that the utility value of the system as a waste heat utilizing system should be improved. As an exemplary configuration that was developed to achieve the task, the configuration disclosed in JP9-88502A is known.
The configuration disclosed in JP9-88502A is as follows: the ratio of the effective screw length of a male rotor and a female rotor composing a screw type expansion turbine with respect to the outer diameter D, that is, L/D, is increased, and an inner end of a suction opening is opened toward an outer circumference surface in the vicinity of the high-pressure-side end of the male rotor and the female rotor.
The invention of JP9-88502A, having this configuration, is intended to reduce inflow loss of a working medium, thereby improve the efficiency, as compared with a conventional configuration in which the working medium flows into a working chamber via a nozzle hole having a limited area.
In such a conventional heat-collecting-type power generation system, however, the amount of heat supplied from a heat source easily varies, thereby there is a problem of an unstable power generation efficiency. Further, there is a problem that such stabilization of power generation efficiency cannot be achieved by the techniques disclosed in JP9-88502A.
The present invention was made in light of this as a background, and it is an object of the present invention to provide a heat-collecting-type power generation system that is capable of maintaining a stable power generation efficiency even if the amount of heat supplied from a heat source varies.
The heat-collecting-type power generation system according to the present invention includes: an evaporator that heats and vaporizes a working medium with heat of a heat source; a displacement-type expander that is driven by the working medium that has been vaporized by the evaporator, the working medium having a high pressure and being in a gas phase; a power generator that is driven in a state of being connected to the expander; a condenser that cools and condenses the working medium in a gas phase that has a low temperature and a low pressure, sent out of the expander; and a circulation pump that draws the working medium in a liquid phase that has been condensed by the condenser, raises the same in pressure, and transports the same to the evaporator, wherein the expander includes a plurality of expansion parts that expand the working medium stepwise, and internal volume ratios of the expansion parts are adjusted in a design phase, so that the expansion parts are configured in such a manner that, in a case where at least one of a suction pressure and a discharge pressure of the expander varies, an overall thermal insulation efficiency is 70 percent or more, in a range of the variation.
With the heat-collecting-type power generation system having such a configuration, since the expander includes a plurality of expansion parts that expand the gas-phase working medium stepwise, it is possible to improve the overall thermal insulation efficiency of the expander. Further, the expander has such a configuration that an overall thermal insulation efficiency is 70 percent or more, in the range of variation of the suction pressure or the discharge pressure, by adjusting the internal volume ratios of the expansion parts in the design phase. The heat-collecting-type power generation system of the present invention, therefore, is capable of maintaining a stable power generation efficiency even if the amount of heat of the heat source varies.
Further, preferably, in the expander, the internal volume ratios of the expansion parts are adjusted so as to be approximately identical to each other.
Here, “approximately identical” is intended to mean that if it can be determined in view of the common general knowledge that respective internal volume ratios of the expansion parts are intended to be identical, the internal volume ratios are considered identical even though there are some differences. With such a configuration, therefore, commonalization of a plurality of expansion parts can be achieved, whereby the design and manufacture are facilitated.
Further, preferably, in the expander, the internal volume ratios are adjusted by changing respective positions of the expansion phase ends in the expansion parts.
With such a configuration, the position of the expansion phase end in each expansion part can be changed by changing the shapes and sizes of the discharge openings, whereby the volumes at the end of the expansion phase can be easily adjusted. In this way, therefore, by changing the shapes and sizes of the discharge openings, the internal volume ratios can be adjusted easily.
Further, the expansion parts may be composed of two stages which are a high pressure side expansion unit and a low pressure side expansion unit.
With such a configuration, production costs of the power generation system can be reduced, while a high efficiency can be imparted thereto.
Further, the evaporator may be configured so as to be heated by supercharged air supplied from a supercharger to an engine.
With such a configuration, electric power to be used in a ship can be supplied by utilizing heat of the supercharged air supplied from the supercharger to the engine.
Further, preferably, the range of the variation of the suction pressure is a range of 1 MPa to 2 MPa both inclusive, and both of the internal volume ratios of the high pressure side expansion unit and the low pressure side expansion unit are 2.6±0.3.
With such a configuration, pressure variation that occurs in the case where heat of supercharged air supplied from the supercharger to the engine and heat of steam generated by the economizer are used can be covered. Further, in this case, the thermal insulation efficiency of the expander can be maintained at 73% upon low-level heat supply, and at 75% upon high-level heat supply. Thus, the amount of generated heat can be increased by 10%.
Further, preferably, each of the expansion parts is a screw type expansion turbine, and the expansion parts and the power generator are housed in one housing.
With such a configuration, windings of the power generator are cooled by using the working medium that is expanded in the expander thereby having decreased pressure and temperature, whereby the efficiency of the power generator can be maintained at a high level. Besides, a structure from which a working medium, a lubricant oil, or the like does not leak out can be achieved, which makes it possible to perform long-term stable operations.
The heat-collecting-type power generation system according to the present invention is capable of maintaining a stable power generation efficiency even if the amount of heat supplied from a heat source varies.